The present invention relates to a new and improved construction of a vacuum tank or vessel, especially for the storage of heat for a long period of time, which is of the type comprising an outer pressure shell and an inner shell having an evacuated intermediate space or chamber.
In order to store thermal energy over a longer time span there was heretofore employed different systems. Thus, in consideration of the beneficial utilization of solar energy there has increasingly become more actual the problem of storing thermal energy, especially the storage of heat over a longer period of time, since it is just during those seasons of the year where the requirement for heat is most prevalent, for instance in the winter, that the solar radiation is not always available. Therefore, there have previously come into use different systems, for instance employing subterranean storage installations. Thus, there have been employed caverns, and specifically in different ways, either in that existing caverns are sealed towards their top and equipped with infeed conduits or lines, or that there were applied metal linings or coverings. These installations are, however, quite complicated and expensive and only then can be used where the ground conditions permit the use of these techniques without having to rely upon additional complicated constructional measures.
A further possibility resides in the use of vacuum technology. When using this technique it is possible to obtain high insulation values, in a manner not even realizable under other conditions with very thick layers of insulation material.
In order to obtain such outstanding insulation values there are required vacuum tanks or vessels. These were heretofore fabricated for a considerable time from steel or materials which did not possess any porosity, preferably from high grade steel. Such type vacuum tanks must, of course, possess an extremely large wall thickness, so as to ensure they are not crushed or collapsed by the external atmospheric pressure. Due to the constructional expenditures and the high material costs such type tanks are much too complicated and expensive for large heat storage installations and also even for smaller heat storage installations, such as are utilized for instance in apartment buildings and other residential structures.